Rapid setting formaldehyde-epoxy resin compositions

ABSTRACT

The ambient curing of glycidyl ether type epoxy resins with primary amines is accelerated by the addition of formaldehyde to the curable mixture.

United States Patent [191 Smith Dec. 3, 1974 RAPID SETTING FORMALDEHYDE-EPOXY 5 References Cited 7 RESIN COMPOSITIONS OTHER PUBLICATIONS Inventor: Harry Smith, a Mich- Chem. Abstract, Vol. 55, p. 25363 b, 1964. 73 Assigneez T Dow Chemical Company Chem. Abstract, V01. 68, p. 31182 U, 1968.

Midland, Mich. Primary Examiner-William H. Shurt [22] Filed: Jan. 18, 1973 Assistant Examiner-T. Pertilla [21] APPL 4 3 Attorney, Agent, or Firm-Benjamin G. Colley v [57] ABSTRACT [52] U.S. Cl. 260/47 EP, 252/182, 260/2 EP. I l 260/2 N 260/292 EP, 260/332 EP, Tile am lent cur ng of glycidyl ether type epoxy resins 760/33 4 EP 260/47 EN 260/49 260/5l with primary amines lS accelerated by the addition of H 7 260/59 formaldehyde to the curable mixture. [51] Int. Cl (108g 30/04, C08g 30/14 [58] Field of Search 260/2 N, 2 EC, 51 EP, 59,

260/49, 47 EN, 47 BO, 51.5, 29.2 EP, 33.4 EP; 252/182, 67 R, 67 PP, 830, 72 R 10 Claims, No Drawings RAPID SETTING F ORMALDEHYDE-EPOXY RESIN COMPOSITIONS This invention relates to curable epoxy resin compositions having increased cure rates.

It is well known in the epoxy resin art that the cure rates of epoxy resins cured with primary amines can be increased or accelerated somewhat with compounds having aromatic hydroxyl groups such as, for example, phenols and the like.

It has now been unexpectedly discovered that small amounts of formaldehyde can be employed to increase the room temperature cure rate of epoxy resins cured with primary amines.

The compositions of the present invention comprise A. an epoxy resin of theglycidyl ether type,

B. an aliphatic or aromatic primary amine-containing compound,- and C. formaldehyde, or a linear or cyclic polymer thereof, or an adduct of formaldehyde and a compound containing a plurality of aliphatic hydroxyl group, wherein the weight ratio of A28 is from about 0.3:] to about 3:1 and preferably from about 1.3:1 to about 2:1 and wherein the weight ratio of epoxy2forma1dehyde contained in component C is from about 3.6: 1- to about 3621 and preferably from about 9:1 to about 18:1.

The present invention also concerns a storage stable epoxy resin composition'comprising A. an epoxy resin having an average of more than one glycidyl ether group per molecule, and

B. formaldehyde or a linear or cyclic polymer thereof capable of releasing formaldehyde at a temperature below about 50C; wherein theweight ratio of A:B is from about 3.6:1 to about 36:1 and preferably from about 9:1 to about 18:1.

The present invention also concerns an improved process in the ambient temperature curing of epoxy resins having an average of more than one glycidyl ether group per molecule with a compound having more than one primary amine group per molecule, the improvement comprising adding to the curable mixture formaldehyde or a linear'or cyclic polymer thereof or an adduct of formaldehyde and a compound containing a plurality of aliphatic hydroxyl groups.

Suitable primary amine-containing compounds include aliphatic amines such as, for example, ethylenediamine, diamino propane,'diethylenetriamine, triethylenetetramine, tetraethylenepentamine, aromatic amines such as, for example, diaminobenzene, methylene dianiline, mixtures thereof and the like.

The formaldehyde or linear or cyclic polymer thereof or an adduct of formaldehyde and a compound containing a'plurality of aliphatic hydroxyl groups is usually employed in a suitable solvent including water; a]- cohols such as, for example, methanol, ethanol, propanol; monoethers of ethylene; and propylene polyglycols.

Any of the well known epoxy resins having an average of more than one glycidyl ether group per molecule are suitably employed in the present invention. Particularly preferred epoxy resins are the liquid epoxy resins. They may be either aliphatic or aromatic epoxy resins, althought the aromatic based epoxy resins are preferred.

Suitable epoxy resins having an average of more than one 1,2-epoxy group per molecule include, for example, those resins represented by the following general formulae:

wherein each A is selected from the group consisting of a divalent hydrocarbon group having from one to four carbon atoms, S--, -SS,

e -'s-. C

O, each. X is independently hydrogen, chloride, or bromine, and n is an integer havingan average value of from about 0 to about 10;

wherein X and X, are independently selected from the group consisting of hydrogen, an alkyl group having from about 1 to about 4 carbon atoms, and a halogen and n is an integer having an average value of from about 0.1 to about 4; 1

wherein R, R and R are independently hydrogen, an alkyl or haloalkyl group having from about one to about four carbon atoms, and a, b, and c are integers, the sum of which is an integer having an average value of from about 3 to about 40;

wherein X and'X' are independently selected from hymethod for their preparation is incorporated herein by drogen, chlorine and bromine. reference.

wherein A is a divalent radical selected from the group -O; R,, R R and R are independently alkylidene groups and R R R and R are independently hydrogen, halogen or alkyl groups having from one to about four carbon atoms.

Suitable cyclic and linear polymers of formaldehyde are, for example, paraformaldehyde, trioxane, mixtures thereof and the like.

The compositions of the present invention can be modified to contain fillers, modifiers, diluents, and the like without detracting from the scope of the invention.

Suitable adducts of formaldehyde with a compound containing a plurality of aliphatic hydroxyl groups include adducts of formaldehyde with alkylene glycols having from about one to about 10 carbon atoms, polyoxyalkylene glycols such as, for example, polyoxypropylene glycol, polyoxyethylene glycol, polyoxybutylene glycol, glycerine, trimethylol propane, pentaerythritol, sucrose, polyglycols prepared by reacting hydroxyl containing compounds with an alkylene oxide such as, for example, ethylene oxide, 1,2-propylene oxide, 1,2- butylene oxide, epichloro hydrin, mixtures thereof and the like.

These formaldehyde adducts and methods for their preparation are more fully described in my copending application, Ser. No. 885,323, filed Dec. 15, 1969 and such application as it pertains, to such adducts and The following examples are illustrative of the present invention and are not to be construed as limiting the scope thereof in any manner.

EXAMPLE 1 Samples were prepared by preparing mixtures con-' taining 3O 5 grams of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of about 190, 3 grams of tetraethylene pentamine, Varying quantities of formaldehyde added as a 55% solution in aqueous methanol (55% CH O, 34%

35 CH Ol-l, 11% H2O).

The various samples were tested for dry adhesion according to ASTM D-l344-57, and a simulated weathering test, conducted according to commercial standards test No. 253-63 which is a modified ASTM D-l344-57 test, wherein each sample is subjected to exposure to water at 25C and s. 25 inches Hg vacuum for 30 minutes followed by exposure to water at 60 psi for an additional 30 minutes and subsequently testing the sample while wet.

The impact resistance was tested according to ASTM TABLE I ADHESIVE TEST Wt. Ratio of Dry Wet Epoxy Resin] Wt. Ratio of T Gel ASTM D-l344-57 CS 253-63 Test Formaldehyde 'Epoxy Resin/ Time Tensile Wood Failure Tensile Wood Failure lmpact No. Solution Formaldehyde Min. psi 71 psi '7! Ft. lb/in 1 (Control) H0 H0 80 315-325 90-100 -150 0-10 9.1 2 20/1 363/] 235-265 95-100 -145 ()20 10.2 3 lO/l l8;2/l 15 280-305 -100 65-475 2-40 4 7/1 12.7/1 2 -220 95-100 N.T.* NT. 88 5 5/1 9/1 1 200-280 100 65-125 060 8.1 6 4/1 7.3/1 l -215 100 120-145 30-60 9.6 7 2/1 3.6/1 0.5 Too fast for practical use without the use of mechanical mixing and application equipment.

N.T. not tested Amine Compound EXAMPLE 2 A glycidyl ether of bisphenol A having an EEW of about 190 was mixed with a, 55 percent solution by weight of formaldehyde in aqueous methanol in a weight ratio of 4 parts of epoxy resin per 1 part by weight of formaldehyde solution. The T this mixture was 24 months.

The above example demonstrates that an epoxy resin composition mixed with formaldehyde solution has exgel time for cellent room temperaturestability.

' EXAMPLE 3 compound. The amine compounds and room temperature T gel time are given in the following Table II.

; TABLE Ii Room Temp. T Gel Time (Min.)

'2,4-l4,4-oxydianiline 4,4'-methylenedianiline' 50 p.514. 14* w w 3s 'D.E.H. i4 is a polyamide curing agent having a viscosity at 40C of about 200 -.6|(J0 cps. a Y I EXAMPLE 4 g A glycidyl ether of bisphenol A having an EEW of about 190 in an amount of grams was mixed with 1.4

grams 37 percent'aqueous solution of formaldehyde.

To this was; added 3. grains of tetraethylenepentamine.

The'Tgel time of' this mixture was 2.5 minutes.

1 i claim: l j

1. A room temperature stable epoxy resin composition comprising r 1 q A. an epoxy resin having an, average of more than one glycidyl ether group permolecule and B. formaldehyde, linearor cyclic polymers thereof, or an adduct of formaldehyde with a compound containing a plurality of aliphatic hydroxyl groups;

wherein the weight ratio of epoxy resinzformaldehyde is from about 3.6:] to about 36: l and wherein component B is dissolved. in a solvent selected from water, alcohols, or monoethers of ethylene polyglycols and propylene 'polyglycol's.

2. The composition of claim 1 wherein the ratio of v epoxy resinzformaldehyde is from about 9:1 to 18:1.

3. The composition of claim 2 wherein component B is formaldehyde.

4. The composition of claim 3 wherein the formaldehyde is in an alcoholic solution.

5. The composition of claim 4 wherein the alcohol i methanol.

6. A curable epoxy resin composition comprising A. an epoxy resin having an average of more than one glycidyl ether group per molecule,

about B. a compound having an average of more than one primary amine group per molecule and C. formaldehyde or a compound capable of releasing formaldehyde at a temperature below about 50C.; wherein the weight ratio of epoxy formaldehyde or the amount of formaldehyde releasable from said compound capable of releasing formaldehyde of from about 3.6:1 to about 3621 and the weight ratio of A18 is from about 0.3:1v to about 3:1 and wherein compo- V nent C is dissolved in a solvent selected from water al-' cohols, or monoethers of ethylene polyglycols and v of an epoxy resin having an average of more than one glycidyl'ether group per moleculewith a compound having an average of more than one primary amine group'per molecule, the improvement which comprises curing in the presence of formaldehyde or a compound capable of releasing formaldehyde dissolved in a solvent selected from water, alcohol, or monoethersof ethylene polyglycols and propylene'glycols at a temperature of less than about 50C. wherein'the weight ratio of epoxy resinzformaldehyde orcompound capable of releasing formaldehyde is from about 3.6:l' to about 

1. A ROOM TEMPERATURE STABLE EPOXY RESIN COMPOSITION COMPRISING A. AN EPOXY RESIN HAVING AN AVERAGE OF MORE THAN ONE GLYCIDYL ETHER GROUP PER MOLECULE AND B. FORMALDEHYDE, LINEAR OR CYCLIC POLYMERS THEREOF, OR AN ADDUCT OF FORMALDEHYDE WITH A CMPOUND CONTAINING A PLURALITY OF AIPHATIC HYDROXYL GROUPS; WHEREIN THE WEIGHT RATIO OF EPOXY RESIN: FORMALDEHYDE IS FROM ABOUT 3.6:1 TO ABOUT 36:1 AND WHEREIN COMPONENT B IS DISSOLVED IN A SOLVENT SELECTED FROM WATER, ALCOHOLS, OR MONOETHERS OF ETHYLENE POLYGLYCOLS AND PROPYLENE POLYGLYCOLS.
 2. The composition of claim 1 wherein the ratio of epoxy resin: formaldehyde is from about 9:1 to about 18:1.
 3. The composition of claim 2 wherein component B is formaldehyde.
 4. The composition of claim 3 wherein the formaldehyde is in an alcoholic solution.
 5. The composition of claim 4 wherein the alcohol is methanol.
 6. A curable epoxy resin composition comprising A. an epoxy resin having an average of more than one glycidyl ether group per molecule, B. a compound having an average of more than one primary amine group per molecule and C. formaldehyde or a compound capable of releasing formaldehyde at a temperature below about 50*C.; wherein the weight ratio of epoxy formaldehyde or the amount of formaldehyde releasable from said compound capable of releasing formaldehyde of from about 3.6:1 to about 36:1 and the weight ratio of A:B is from about 0.3:1 to about 3:1 and wherein component C is dissolved in a solvent selected from water, alcohols, or monoethers of ethylene polyglycols and propylene polyglycols.
 7. The composition of claim 6 wherein the epoxy resin: formaldehyde or formaldehyde releasable from said compound capable of releasing formaldehyde is from about 9:1 to about 18:1 and the weight ratio of A:B is from about 1.3:1 to about 2:1.
 8. The composition of claim 7 wherein component C is formaldehyde.
 9. The composition of claim 8 wherein the formaldehyde is in an alcoholic solution.
 10. In a process for the ambient temperature curing of an epoxy resin having an average of more than one glycidyl ether group per molecule with a compound having an average of more than one primary amine group per molecule, the improvement which comprises curing in the presence of formaldehyde or a compound capable of releasing formaldehyde dissolved in a solvent selected from water, alcohol, or monoethers of ethylene polyglycols and propylene glycols at a temperature of less than about 50*C. wherein the weight ratio of epoxy resin:formaldehyde or compound capable of releasing formaldehyde is from about 3.6:1 to about 36:1. 